What is a subdomain?

A subdomain is a name in front of a domain, like shop.example.com. It behaves as a separate address but lives inside a domain that already exists. When a tool gives you a free address for your new site, it is usually giving you a subdomain of theirs.

Free subdomains are genuinely useful and there is nothing second class about them. What they are not is yours in the way a registered domain is. If the parent domain has a problem, every subdomain on it shares the problem, which is exactly why user sites and company sites should never live on the same one.

That is why apps published from Ura live on ura.build rather than on ura.dev. A difficulty with one published app can never reach the company, and a difficulty with the company can never take down somebody's live site.